In the past two decades the commercial use of electron beam energy machines in metalworking has grown considerably. A high electrical potential propells electrons at high energies toward a workpiece typically within a vacuum chamber, to cause melting. One of the most useful applications of electron beam energy has been for the drilling of holes in workpieces. The stream of electrons, which is precisely focused by means of magnetic fields, has been found capable of rapidly drilling rather small holes by a combination of melting and vaporization. Because of the high energy densities, of the order of 72.times.10.sup.6 watts/cm.sup.2, there is little general heating of the workpiece, inasmuch as a typical hole is created in the workpiece in a fraction of a second.
To achieve industrial utility, the manufacturers of electron beam machines had to make them durable. To be durable, the electron-producing filaments of the machines must be long lasting, and the energy content and concentration of the beam must be constant. Such goals have not been achieved without difficulty. The environment within the chamber where drilling takes place is characterized by flying droplets of molten metal and condensing metal vapor. The metal which is expelled from the workpiece tends to fly towards the electron gun components that create and guide the electron stream towards the workpiece. Therefore, various protective devices have been developed to protect them.
Generally, these devices comprise metal shields, typically in the form of rotating discs having adjacent scrapers remove the metallic debris which lands on them. The shields provide a space through which the electron beam can escape from the gun and impinge on the workpiece. While this hole is kept small, it is of necessity larger than the diameter of the beam for simple mechanical reasons, and to allow for purposeful deflection of the beam. Consequently, there is some tendency for a limited amount of debris to travel generally along the path of the beam, to the inside of the gun. In anticipation of this, there are provided other shields in the interior of the gun to capture this small amount of debris. They are similar in function to the primary shields.
The foregoing type of system works well for general applications. In most hole drilling, the conical shape of the metal expulsion is such that the bulk of it impinges on the primary shields. But drilling holes of very small diameter and great relative depth, particularly great quantities of workpiece metal expulsion are directed back through the primary shield opening, into the insides of a conventional electron beam gun. It has been found that the greater quantities of metal deposited in the insides of the gun cannot be accommodated by the internal shielding known in the prior art. Therefore, an improvement in the design of the drilling machine was necessitated.